Effects of Recycling Periods on Physical and Mechanical Properties of CMP and NSSC Pulps

The effect of recycling on physical properties of lignin rich chemimechanical pulp (CMP) and neutral sulfite semi-chemical (NSSC) pulp was evaluated. The pulps were exposed to recycling treatment for three times without any further refining and the fines were conserved. The results indicated that some physical properties like tensile strength، tensile energy adsorption (TEA)، burst strength، apparent density and compression strength were decreased by recycling due to hornification followed by loss in fiber flexibility and swelling which give rise to interfiber bonding loss. However the opacity and light scattering coefficient presented gain through recycling. Besides، the bending stiffness، air permeability and roughness increased due to recycling. The observations generally indicated that the CMP and NSSC pulps behavior under recycling is much similar to that of chemical pulp rather than mechanical pulps.